The transforming gene of simian sarcoma virus (SSV), v-sis, directs the synthesis of a protein of 28,00 daltons, p28sis. Biochemical characterization of p28sis has revealed that the molecule is a membrane-associated protein which is synthesized in the endoplasmic reticulum, glycosylated, and then transformed to the cell surface where it is cleaved into proteins of 11,000 and 20,000 daltons. The exact glycosylation site of p28sis has been identified and the site of its cleavage is known to within 10-15 amino acids.